The effect of temperature on the surface tension of soluble and insoluble surfactants was investigated at an air-water interface. Equilibrium surface tension measurements were performed using the Wilhelmy plate technique in which both temperature and concentration were varied systematically. Insoluble surfactants (oleyl alcohol and hemicyanine) and soluble surfactants (Triton X-100 and sodium dodecyl sulfate (SDS)) were used since they are commonly used in hydrodynamic experiments in which the effects of surfactants on free surface dynamics are studied. The principal result of this investigation is that the surface tension of the above-mentioned surfactants decreases linearly with temperature, independent of concentration, with the exception of oleyl alcohol whose surface tension becomes relatively independent of temperature above 23 °C. The adequacy of standard models for surfactant behavior in describing these data is considered.

Health-care workers, laboratorians and overdose prevention centers rely on commercial immunoassays to detect the presence of fentanyl; however, the cross-reactivity of fentanyl analogs with these kits is largely unknown. To address this, we conducted a pilot study evaluating the detection of 30 fentanyl analogs and metabolites by 19 commercially available kits (9 lateral flow assays, 7 heterogeneous immunoassays and 3 homogenous immunoassays). The analogs selected for analysis were compiled from the Drug Enforcement Administration and National Forensic Laboratory Information System reports from 2015 to 2018. In general, the immunoassays tested were able to detect their intended fentanyl analog and some closely related analogs, but more structurally diverse analogs, including 4-methoxy-butyryl fentanyl and 3-methylfentanyl, were not well detected. Carfentanil was only detected by kits specifically designed for its recognition. In general, analogs with group additions to the piperidine, or bulky rings or long alkyl chain modifications in the N-aryl or alkyl amide regions, were poorly detected compared to other types of modifications. This preliminary information is useful for screening diagnostic, forensic and unknown powder samples for the presence of fentanyl analogs and guiding future testing improvements.